Myocardial and peripheral catecholamine responses to acute coronary artery constriction before and after propranolol treatment in the anaesthetised dog

Abstract

The left anterior descending coronary artery was constricted for eight minutes on two occasions in 13 anaesthetised open-chest dogs. One group (n = 8) was studied before and afer 1 mg . kg-1 propranolol intravenously; a second group (n = 5) served as controls. Simultaneous blood samples were drawn from arterial and coronary sinus catheters for measurement of lactate and catecholamine concentrations. In controls, coronary artery constriction resulted in a reproducible fall in fractional myocardial lactate extraction and an increase in left atrial pressure, but caused no significant changes in blood pressure, heart rate or plasma concentrations of noradrenaline, adrenaline, or dopamine. In the treated group, heart rate was reduced but blood pressure was the same after propranolol; both remained unchanged during constriction and after release. The fall in fractional lactate extraction was abolished by propranolol. Arterial noradrenaline increased significantly after propranolol, fell during constriction and rose again after release. A similar trend was observed in coronary sinus noradrenaline. Reversible myocardial ischaemia is not associated with peripheral or myocardial release of catecholamines. Pre-treatment with propranolol appears to exert a protective effect on the myocardium even during reversible ischaemia. Although peripheral noradrenaline levels are increased after propranolol, this increase is not maintained during coronary artery constriction.